Complete or partial protection was conferred to a significant number of strain-2 guinea pigs by the passive transfer of antibodies reactive to antigens from line-10 cells. Immunoglobulins were administered i.d. and injected sites were subsequently challenged with line-10 cells. Protection was greater if normal syngeneic peritoneal cells were administered in addition. ADCC was demonstrated in vitro against viable guinea pig line-10 hepatocarcinoma cells using syngeneic mineral oil-induced peritoneal exudate cells from normal guinea pigs and rabbit antibodies to line-10 cells. When 51 syngeneic sera from line-10 tumor resistant guinea pigs were similarly tested, a large proportion of these sera also mediated ADCC. These experiments suggested that syngeneic line-10 specific antibodies in sera of tumor resistant guinea pigs as well as xenogeneic immune sera were capable of mediating ADCC in vitro. Studies are planned to determine the cell type involved. Suppression of growth of the line-10 tumor was achieved after the simultaneous injection of line-10 cells and heat-killed Staphylococcus aureus and Propionibacterium acnes (C. parvum). Immunity developed to subsequent challenges with line-10 cells but not to other syngeneic tumors. Multiple intratumoral injections of heat-killed S. aureus, Listeria monocytogenes, and P. acnes were therapeutically effective against six day old tumors. Treatments with other bacterial strains are also underway. The anti-tumor effects of non-viable bacteria were similar in many ways to those of living BCG or bacterial products suspended in oil droplets. A series of sequential purification procedures including affinity chromatography and electrophoresis in acrylamide gels were employed to prepare antigenic components that differentiated between antigens in line-10 cells and BCG. Some of the fractions isolated were radiolabeled and were found to bind to antibodies to BCG and to line-10 cells but not to antibodies in sera from rabbits immunized with other bacteria or other syngeneic tumors.